These tiny, high-quality motors are intended for use at 6 V. In general, these kinds of motors can run at voltages above and below this nominal voltage, so they should comfortably operate in the 3 – 9 V range. Lower voltages might not be practical, and higher voltages could start negatively affecting the life of the motor. All of the micro metal gearmotors have the same physical dimensions, but they come in a wide range of gear ratios—from 5:1 up to 298:1—and let you choose between two different motors: high-power (HP) and standard.